INFLUENCE UPON CONTRACTILITY 29 



been made to show that the heart is automatic, and 

 that its action depends upon the constitution of the 

 blood. Ho well* says a strip of vena cava from the 

 terrapin's heart may be kept in rhythmic action for 

 two or more days if it is immersed in a bath con- 

 taining sodium chloride and calcium or potassium 

 chloride. This renders very improbable the state- 

 ment of Kronecker that cardiac tissue only beats so 

 long as serum albumen is supplied to it. It also 

 makes it evident that the energy is derived from 

 within the cardiac tissue, and that if the tissue is 

 supplied with an adequate stimulus the beat will 

 continue until the source of the energy is consumed. 

 Wilsonf also states that a strip of muscle from the 

 apex of a terrapin's heart was kept alive by placing 

 it in normal serum for several days ; normal serum, 

 however, did not keep it in contraction, but a 

 regular rhythmic contraction was induced by the 

 addition to the serum of some calcium chloride. 

 On the other hand, LoebJ concludes that the 

 presence of calcium and potassium chloride is not 

 essential for the maintenance of rhythmic contrac- 

 tion, but that their constant presence is necessary 

 indirectly by neutralising the toxic effect of sodium 

 chloride, which is present in blood and sea-water, 

 and which he asserts is toxic to all contractile 

 tissues. 



* Loc. cit. t Amer. Jour. PhysioL, 1893, ii., 82-126. 



J f finger's Archiv, Ixxx., 229-232. 



